Fortified rosin size and paper sized therewith



Unite States Patent 2,934,468 FORTIFIED ROSIN SIZE AND PAPER SIZED THEREWIT 13 Claims. (Cl. 162-180) This invention relates to a novel fortified rosin size, i.e.

rosin size which when applied in paper-making manufacture yields paper and other water-laid cellulose webs of improved resistance to penetration by aqueous fluids such as water, ink, and particularly lactic acid. The invention includes the size itself, water-laid cellulosic webs sized by a content thereof, and methods for making the size and the webs. Cellulose webs having high resistance to penetration by aqueous lactic acid solutions (representative of food acids in general) are required in the manufacture of milk containers, ice cream containers, paper cups, food wrap paper, etc.

It is known that rosin can be improved (in terms of the water, etc. resistance it imparts to cellulose fibers sized therewith) by pre-reacting the rosin with an alpha,beta unsaturated dicarboxylic anhydride containing not more than 6 carbon atoms such as maleic anhydride, maleic anhydride-dehydrated citric acid mixtures, etc. (cf. U.S. Patent Nos. 2,383,933, 2,628,918, and 2,684,300; also application Serial No. 359,445 filed on June 3, 1953, now U.S. Patent No; 2,771,464). The improvement effected by such prereaction is generally termed fortification, and the size prepared from the treated rosin is generally termed fortified rosin size. The anhydride is reacted in small but effective amounts, generally between A to A,

when irreversibly reacted with rosin, also acts as fortifying agent, greatly improving the elfectiveness of size prepared therefrom. We have found that when formalde' hydeis prereacted with the rosin and the rosin converted to size, the lactic acid resistance imparted by the size is often about doubled. In addition, the water resistance and ink resistance imparted are usually substantially improved. The amount of formaldehyde required for this effect is small, generally to 7% of the weight of the rosin, equivalent to about V to mol.

This discoveryv was unexpected as the normal action of formaldehyde is to make compounds into which it is introduced more hydrophilic. The reacted formaldehyde present in liquid sizes prepared according to the present invention imparts the advantageof decreasing and often preventing the tendency of the size to crystallize. As a result, liquid sizes of the present invention can be held in storage longer than would otherwise be the case, thus permitting more flexible papermill operations.

The sizes of the present invention are prepared by irreversibly reacting a rosin with a small but eifective amount of formaldehyde for the purpose described followed by saponifying the treated rosin in normal manner with aqueous alkali metal alkali solution to form liquid size which may be dried. According to present day commercial practice, the amount and strength of aqueous alkali solution employed is predetermined so that the saponification product contains from about 60% to 80% sizing solids by weight, and up to about 30% of free rosin acids, based on the weight of rosin acids originally present in the rosin. The rosin acids are thus at least 70% saponified and are usually substantially completely or 100% saponified when intended for conversion into dry size form. The particular manner in which the rosin is con.-

ice

. a 2 verted into size, however, is not a primary feature of the invention.

The size is used in the same manner as ordinary rosin size by forming a dilute aqueous suspension of papermaking cellulose fibers, adding a dilute aqueous solution of the size, precipitating the size on the fibers by alum, sheeting the fibers to form a web, and drying the web to form paper. The size on addition to the pulp may contain other materials such as starch, locust bean gum, alkali-stable wax size, pitch dispersants of the naphthalenesulfonic acid type known as Tanak A, casein, clay, etc.

A perceptible improvement resulting from the presence of irreversibly reacted formaldehyde has been noticed when as little as ,Qgmol of formaldehyde is reacted per mol of rosin, so that evidently there is no amount of formaldehyde, however small, which will not produce some benefit. At the other extreme, the amount of formaldehyde added need not be materially in excess of mol calculated on the same basis, as in this upper range the benefit imparted by each increment of formaldehyde becomes less significant. In practice, we have found it preferable to react the rosin with between about to /3 molar equivalents of formaldehyde 1% to 3.3% by weight) as in this range the benefits associated with the presence of the formaldehyde are' most apparent, and waste of the formaldehyde is minimized. It will be understood, however, that it is within the scope of the invention to prepare the size by reacting the rosin with a larger amount of formaldehyde and blending the reaction product with untreated rosin to decrease the formaldehyde content of the blend within the range stated.

The mechanism by which the formaldehyde reacts is not known and I do not wish to be limited to any theory. Theoretical chemistry indicates, however, that the formaldehyde may react simultaneously according to several reactions, of which the following equations indicate two of the possible initial stages:

0 O OH OCH2 Prin's reaction 0 0 OH Abietic acid C O OH HzQH Reaction with active hydrogen atom Theory further indicates that continued heating converts any such compounds present into complex polymer form. The foregoing equations have not been proved and are presented for whatever value they may have in assisting an understanding of the invention. It is evident, however, thatthe formaldehydereaction productis a complex mixture in which the formaldehyde is substantially irreversibly combined and that the sizes obtained therefrom are most conveniently described in terms of its preparation.

The irreversible reaction of rosin with formaldehyde begins at a temperature of approximately 135 C., below which only a loose association complex forms which is of no substantial value in the present invention, the presence of which may be determined by the phenylhydrazine test for free formaldehyde. Good results are obtained up to about 250 C., and even higher temperatures may be used with however, some decomposition resulting in decreased effectiveness. In plant practice, we prefer to carry out the reaction at a temperature between about 190 C. and 230 C., the reaction taking place rapidly while darkening of the rosin and formation of decomposition products'are minimized. The reaction should be continued until the amount of formaldehyde which has irreversibly reacted is within the range indicated. Unreacted formaldehyde is tolerated and is lost with the. white water during the sheeting step.

The formaldehyde may be added to the rosin in any convenient form. Formalin (37% aqueous formaldehyde solution), gaseous formaldehyde or trioxane are suitable when a closed reaction vessel is available. The reaction may be performed in an open vessel at atmospheric pressure when the formaldehyde is paraformaldehyde (added either as such or dissolved in the alcohol mixture known as Formcel), and for this reason paraformaldehyde is preferred.

The rosins used in the preparation of sizing agents, according to the present invention include gum rosin, wood rosin, and the newly developed rosin known as tall oil rosin (i.e., the rosin remaining after removal of the fatty acids from tall oil by fractional distillation), for

haps as the result of the reaction of rosin carboxyl groups With methylol groups introduced by the paraformaldehyde. The rosin was then cooled to 140 C. and saponified by adding thereto with stirring 190 gm. of 13% aqueous sodium hydroxide solution. A liquid rosin size of 70% solids and 19% free rosin acid content was obtained.

The foregoing procedure was repeated for purposes of control using the same rosin and the same volume of caustic solution except that the step of adding formaldehyde was omitted and a slightly stronger (14.5%) sodium hydroxide solution was used. The increase in strength of the caustic solution was required by the higher acid number of the rosin so as to obtain a size of the same free acid content.

The two sizes were tested according to standard laboratory procedure by preparing an aqueous slurry of bleached 60% :40% sulfitezsoda pulp at 0.6% consistency and adding thereto 2% of the size diluted to about 5% solids with water, followed by the addition of 2% of alum. All weights represent solids based on the dry weight of the fibers.

The sized fibers were sheeted on a British handsheet A machine at 200 lb. basis weight (lb. per x 40"/500 ream) and dried on a laboratory drum drier at 240 F. for four minutes. The sheets were conditioned at 73 F. and humidity for 24 hours and tested to determine their resistance to penetration by 20% aqueous lactic acid solution at 100 F., fountain pen ink, and water. The lactic acid values were obtained by penescope, the ink values. by automatic reflectometer using the under side of the sheet as the base. and the water adsorption values by the total immersion method, the time of immersion being 15 minutes at 73 F. Handsheets were similarly made at a basis weight of 50 lb. for determination of ink resistance values.

which standards have been established by the U.S. Department of Agriculture. rosins prepared by condensing a natural rosin of an alpha, beta unsaturated dicarboxylic anhydride, etc., as described above, and pure abietic acid itself.

The invention will be more particularly illustrated by the examples. These examples represent specific embodiments of the invention and are not to be construed as limitations thereon.

Example 1 The following illustrates theincrease in resistance to aqueous fluids imparted by rosin size containing a preferred amount of combined formaldehyde according to the present invention.

To 302 gm. (1 mol) of S grade tall oil rosin at 140 C. in an open glass vessel heated by an electric mantle and provided with slow agitation was added 6.0 gm. /s mol) of paraforrnaldehyde coarse powder. The paraformaldehyde dissolved in about one hour with slow stirring. The temperature of the reaction mixture was then raised over a period of one hour to 220 C. and maintained at that temperature for another hour, at the end of which time the paraforrnaldehyde had irreversibly reacted. Analysis of the mixture by the phenylhydrazine method showed 0.004% free formaldehyde. The acid number of the rosin (corrected'for addition of the formald y e) es o ndto .ha eds re s Slightly, p

The table shows the presence of only 2% or l/s mol Additional rosins include the 50 of reacted rosin nearly doubled the resistance of the paper to penetration by lactic acid solutionand produced a substantial increase in the resistance of the sheets to absorption of water and penetration by ink.

The. foregoing tests were essentially repeated, the significa'nt change being the addition of 0.2% of petroleum wax emulsion size along with the rosin size (wax solids based on the dry weight of the fibers). The presence of combined formaldehyde in the rosin component did not adversely affect the lactic acid, water and ink values.

Samples of the twosizes as prepared (i.e., at 70% solids and 19% free acid content) were placed in an incubating oven at .C. and observed for crystallization. The control size started to develop crystalsin five days and turned into a substantially solid mass of crystals in 20 days, but the test sample (which contained the 2% of reacted formaldehyde) remained entirely free from crystals for 25 days. i

' Example 2 The following illustrates the preparation of an improved fortified rosin size according to the present invention by simultaneously reacting formaldehyde and a minor amount of an alpha, beta unsaturated dicarboxylic anhydride with rosin followed by saponification. A mixture was prepared in the apparatus of Example 1 from 302 gm. (1 mol) of S-grade tall oil rosin at 0.,

15.1 gm. of maleic anhydride (0.15 mol), and 11 gm, of 55% methyl Fornicel (a 55% by weight solution of paraformaldehyde in methanol-water), the amount of the formaldehyde thus being equivalent to 0.2 mol based on the rosin. The methanol and water flashed off. The

temperature was slowly raised to 220 C. and maintained at that point for one hour. At the end of this time, reaction of the maleic anhydride and the formaldehyde was substantially complete.

The molten fortified formaldehyde-containing rosin was saponified to form a 70% solids liquid size containing 19% free rosin acid as described in Example 1.

A control size was prepared by repeating the above procedure except that no formaldehyde was added and the amount of caustic used for saponification was adjusted so as to produce a liquid size of a same free acid content.

The lactic acid resistance imparted by the sizeswas determined by the general method of Example 1 except that the pulp was bleached northern kraft, and the sheets were formed on a Nash handsheet machine. Results are as follows:

The results show that adding formaldehyde along with the maleic anhydride very materially increased the fortifying effect. Other laboratory data show that similar results are obtained when the rosin and maleic anhydride are reacted separately in either sequence.

Example 3 The following tests were made to illustrate the comparative effectiveness of formaldehyde as fortifying agent The, table shows (Nos. 1 and 3) that while untreated gum rosin size is markedly superior to untreated tall oil rosin size, fortification of the tall oil rosin with formaldehyde (No. 4) increased the effectiveness of the size so The following illustrates the use of aqueous formalin as the fortifying agent.

on tall oil rosin using gum rosin as the standard. Tall oil rosin is the rosin which of all the commercial rosins usually imparts lowest water-resistance and s0 is the most important rosin to improve.

A series of liquid sizes was made according to the general method of Example 1 employing rosin, S-grade tall oil rosin as representative of commercial tall oil rosin and WG gum rosin as representative of commercial gum rosin. The formaldehyde was added in the form of paraformaldehyde in amounts shown in the table below and in each instance the sizes were prepared at 70% solids and 19% free acid content by the general method of Example 1, the sizes were tested by the method of Example 1, except that the amount of size added was 2.5% of the dry weight of the fibers and the size was precipitated by 3% of alum.

The efiiciency of each size was determined on a 60% :40% bleached sulfite:bleached hardwood pulp, the hardwood component of which had been bleached with chlorine dioxide. It is well known that this pulp is unusually difiicult to size.

The sheets were prepared on a British hand sheet machine (basis weight 200 lb. per 40x25"/500 ream) and were dried for four minutes at 240 F. and conditioned as described above. Results are as follows.

302 gm. (1 mol) of N-grade wood rosin was placed in a laboratory autoclave and 16.3 gm. (0.2 mol) of 37% aqueous formalin added thereto. The autoclave was sealed, brought to a temperature of 220 C., allowed to remain at that temperature for one hour, and then allowed to cool. Analysis of the rosin by the phenylhydrazine method showed a content of 0.0003% -by weight. j

The treated rosin was formed into a liquid size at sizing solids and 19% free acid content and tested by the method of Example 1 in comparison with corresponding wood rosin liquid size which, however, contained no combined formaldehyde. The sheets containing the size prepared'from the treated rosin were markedly superior to the control sheets in their lactic acid resistance values.

Example 5 The following illustrates the effect on the lactic acid resistance imparted by variations in the proportion of formaldehyde reacted.

The general procedure of Example 1 was followed using 8 grade tall oil rosin, and the amount of caustic used for saponification was adjusted so as to obtain 'in each instance a 70% solids size containing 19% free rosin acids. t

The resistance of the sheets to penetration by lactic acid was determined by the method of Example 1, except that 60/40 bleached sulfite and chlorinedioxide bleached hard wood pulp and 2 /2% sizes and 3% alum were used based on the dry fibers. Results are as follows:

CHZO React. Lactic Acid Resist. Water Absorption Mols Percent Secs. Percent Percent Percent er. Gain Deer The results indicate that most efiicient utilization of the formaldehyde occurs within the range li A mol of formaldehyde per mol of rosin.

Example 6 The effect of the fortifying pretreatment of the present invention upon the tendency of the liquid rosin sizes to crystallize was determined as follows. Tall oil rosin was employed for this test because this yields liquid sizes which normally display greatest tendency to crystallize. A series of sizes was prepared by fortifying S-grade tall oil rosin according to the method of Example 1 in the presence or absence of maleic anhydride as supplementary fortifying agent as shown in the table below. The rosins were converted into liquid size at 79% solids and 24% free .acid content, experience having shown that liquid sizes having this total solids and free acid content display most pronounced tendency towards crystallization on storage.

The liquid sizes were tested by taking 2 ounce samples of each size, tightly stoppering the bottles, and incubating the bottles in an oven maintained at 70 C. The samples were, observed everyday for evidence of crystallization, andthe observations were discontinued when crystallizatiori reached 50%. j

' Ihe percent of crystallization was determined in each instance by viewing a sample of the size through a micro.- scopeand estimating the proportion of the field occupied bycryst als. A crystallization value of is about the most that can be tolerated in a paper size. Results are of alum, sheeting said fibers to form a web,

said web.

9. A liquid rosin size containing at least 60% of size as follows: solids by-weight and up to 30% of free rosin acids based CH2O React. MaleicAnh. Percent Crystallization j Reacted No. 7 V

Mols 1 Percent Mols 1' Percent One Two Three Seven Forty Day Days Days Days Days None 0 2 1O 50 0. 0 0 2 10 50 1 None 0 0 2 10 60 2 None 0 0 0 2 40 3.3 None 0 0 0 0 0 5 None 0 0 0 0 0 2 0.15 0 0 0 0 0 Per mol of rosin. 9 Based on weight of rosin Comparison of tests Nos. 1 and 3 shows that even 0.1

mol of formaldehyde had a clear'effect in inhibiting crystallization and that 0.33 mol of formaldehyde (No. 5) entirely prevented crystallization. The table further shows. (No. 7) that /s of a mol of formaldehyde was sufficient to prevent crystallization of the size prepared from fortified rosin.

Example 7 A dry size was prepared according to the present invention by reacting 302 gm. of wood rosin (N grade) with .6 gm. of paraformaldehyde at 250 C.. for minutes, after which the reaction product was saponified with 38 gm. of sodium hydroxide in 175- gm. of boiling water.

The resulting liquid size was cooledand dried on a steam-heated laboratory drum drier provided with scraper knife. Flakes of excellent quality dry size were obtained.

I claim: 8

l. A liquid rosin size containing at least 60% of size solids by weight and up to 30% of free rosin acids based on the weight of'rosin acids originally present in the rosin, and being the alkali metal alkali-saponification product of the material resulting from the irreversible reaction of a rosin with a small but. effective amount of. formaldehyde as fortifying agent. 7

l 2. A size according to claim 1 wherein the amount of formaldehyde is in the range of one-tenth to one-third molar equivalents.

3. A'size according to claim 1 wherein the reacted formaldehyde is paraformaldehyde.

41A size according to claim 1 wherein the rosin is tall oil rosin.

5. A size according tov claim. 1 wherein the formaldehyde is reacted at a temperature between 190 C. and 230 C.

6. A methodof manufacturing a sized water-laid cellulosic web of improved resistance to penetration by aqueous fluids which comprisesforming adilute aqueous suspension of paper-making cellulose fibers, adding thereto liquid size according. to claim 1 as sizing agent for the fibers, precipitating said size onsaid fibers by the action of alum, sheeting said fibers to form a web, and drying said web.

7. A liquid. rosin size containing at least 60% of size solids by,weight and up to 30% of free rosinacids based on the weight of rosin acids originally present in the rosin, and. being the alkali. metal alkali-saponification product of theQmaterial resulting from the irreversible reaction of a rosin with small but effective amounts of an alpha-beta unsaturated. dicarboxylic anhydride containing not more than six carbon atoms and formaldehyde as fortifying agents. 3

8. A method of manufacturing a sized water-laid celluon the weight of rosin acids originally present in the rosin, and being the alkali metal alkali-saponification product of the material resulting from the, irreversible reaction of tall oil rosin and small but effective amounts of maleic anhydride and formaldehyde as fortifying agents.

10. A dry rosin size of increased sizing efiiciency consisting essentially of the material produced by irreversibly reacting a rosin with a small but effective amount of formaldehyde as fortifying agent, substantially completely saponifying it with an aqueous alkali metal alkali, and drying the resulting liquid size.

11. A dry rosin size of increased sizing efliciency consisting essentially of the material produced by irreversibly reacting a rosin with small but effective amounts of an alpha-beta unsaturated dicarboxylic anhydride scontaining not more than six carbon atoms and formaldehyde as fortifying agents, substantially completely saponifying it with an aqueous alkali metal alkali, and drying the re.- sulting liquid size.

12. Paper of improved resistance to penetration by aqueous fluids comprising a water-laid web .of cellulosic fibers uniformly carrying sizing amounts of an alumprecipitated fortified rosin size, said size being thealkali metal alkali-saponification product of the material resulting from the irreversible reaction of a rosin with a small but effective amount of formaldehyde as fortifying agent.

13. Paper of improved resistance to penetration by aqueous fluids comprising a water-laid web of cellulosic fibers uniformly carrying sizing amounts of an alum-precipitated fortified rosin size, said size being the. alkali metal alkali-saponification product of the material resulting from the irreversible reaction of a rosin with small but eifective amounts of an alpha-beta unsaturated dicarboxylic'anhydride containing not more than six carbon atoms and formaldehyde as fortifying agents.

References Cited in the file of this patent UNITED STATES PATENTS 2,197,383 Outterson Apr. 16, 1940 2,301,298 Light et al. Nov. 10, 1942 2,309,346 Landes et al. Jan. 26, 1943 2,374,657 Bain May 1, 1945 2,385,794 Chappell Oct. 2, 1945 2,572,071 St. Clair et al. Oct. 23, 1951 2,628,918 Wilson et al. Feb. 17, 1953 2,684,300 Wilson et al. July 20, 1954 2,744,889 Gayer May 8, 1956 FOREIGN PATENTS I 200,689 Switzerland Jan. 2, 1939 149,233 Australia Dec. 1, 1952 thereof, under the heading "CH O heated" and subheading "'Mols UNITED STATES PATENT OFFICE CERTIFICATE ()F CORRECTION Patent No, 2,934 468 April 26 196.0

Edward Strazdins It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, line 74 Example 3., in the table third column last line, for "1/3" read l 5 Signed and sealed this 20th day of September 1960.

(SEAL) Attest:

KARL H AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents 

1. A LIQUID ROSIN SIZE CONTAINING AT LEAST 60% OF SIZE SOLIDS BY WEIGHT AND UP TO 30% OF FREE ROSIN ACIDS BASED ON THE WEIGHT OF ROSIN ACIDS ORIGINALLY PRESENT IN THE ROSIN, AND BEING THE ALKALI METAL ALKALI-SAPONIFICATION PRODUCT OF THE MATERIAL RESULTING FROM THE IRREVERSIBLE REACTION OF A ROSIN WITH A SMALL BUT EFFECTIVE AMOUNT OF FORMALDEHYDE AS FORTIFYING AGENT.
 10. A DRY ROSIN SIZE OF INCREASED SIZING EFFICIENCY CONSISTING ESSENTIALLY OF THE MATERIAL PRODUCED BY IRREVERSIBLY REACTING A ROSIN WITH A SMALL BUT EFFECTIVE AMOUNT OF FORMALDEHYDE AS FORTIFYING AGENT, SUBSTANTIALLY COMPLETELY SAPONIFYING IT WITH AN AQUEOUS ALKALI METAL ALKALI, AND DRYING THE RESULTING LIQUID SIZE. 